The invention relates to POTS splitter devices that are mounted externally to digital subscriber loop access multiplexers in remote terminal and central office equipment racks.
Providing high rate digital transmissions over the local subscriber loops of telephone companies is advantageous since the infrastructure for such local subscriber loops is currently in existence. High-rate digital subscriber loop (DSL) data services have been implemented using transmission technologies such as asynchronous DSL (ADSL), synchronous DSL (SDSL), high-speed DSL (HDSL), and very high-speed DSL (VDSL), which are generally referred to as xDSL.
High-speed digital transmissions available via xDSL share the same DSL with analog telephony (i.e., plain old telephone service (POTS)). POTS and xDSL are transmitted on the same analog telephone lines using frequency division multiplexing. For example, POTS transmissions generally occur in a frequency range 12 of 0 Hertz (Hz) to 4 kiloHertz (kHz). xDSL transmissions use higher frequencies such as 20 kHz to 1.1 MegaHertz (MHz). With reference to FIG. 1, xDSL frequencies 14 use higher frequency bands that do not overlap with the analog voice or POTS frequency range. This allows for the use of high-pass filters (HPFs) and low-pass filters (LPFs) to separate the POTS and xDSL signals at both ends of the DSL transmission line. Separate frequency bands can also be allocated for upstream xDSL transmissions toward the network (e.g., a central office (CO) or local exchange (LE)) and downstream xDSL transmissions toward customer premises. Thus, xDSL permits data transfer on existing telephone lines in both directions simultaneously, and does not interfere with analog telephone transmissions.
To provide DSLs to customer premises, customer premises xDSL equipment is needed, as well as POTS equipment for voice calls. As shown in FIG. 2, telephone company equipment (e.g., a remote terminal (RT) or CO) which accommodates xDSL data transmissions is also needed. The customer premises 18 can comprise, for example, a network interface device (NID) 20 connected to an analog telephone line 22. The NID 20 comprises a LPF or POTS splitter 24 that filters high frequency xDSL signals and passes low frequency POTS signals to POTS equipment such as telephones 26. xDSL modems use a HPF to attenuate POTS signals to recover the data signals in the higher frequency bands.
With reference to FIG. 3, the RT or CO 30 receives signals from and provides signals to the telephone line 22 which can have POTS signaling, as well as xDSL data transmissions. The RT or CO 30 generally comprises channel banks (CBs) 32 or other voice termination equipment for processing voice calls, and a DSL access multiplexer 34 hereinafter referred to as a DLSAM for processing xDSL transmissions. Different types of DSLAMs include, but are not limited to, a central office DSLAM, a remote DSLAM and remote ADSL multiplexers.
The RT 30 is generally contained in a cabinet containing the RT termination equipment (e.g., channel banks), an auxiliary power source and protection devices to protect telephony devices against unwanted voltage and current. The cabinet is located remotely with respect to the CO. The CO comprises termination and switching equipment, much of which is mounted in equipment racks. The amount of rack space available for accommodating equipment such as DSLAM to provide new services is limited and must be used efficiently.
With continued reference to FIG. 3, DSLAMs 34 are typically provided with circuitry 38 for passing POTS signals to voice call processing circuits such as CBs 32, and for passing xDSL data to xDSL processing circuits. A LPF can be used to filter xDSL data signals from incoming telephone lines and pass POTS-only signals to the channel bank or telephone. HPFs are provided on-site at the customer premises and at the CO or RT to filter out POTS signals and pass only the xDSL signals to the appropriate processing circuits. In existing systems, POTS splitters are used in the on-site NID 20 and in a DSLAM or POTS splitter rack at a CO or RT to filter POTS signals.
The processing of POTS and xDSL signals at an RT or CO will now be described in further detail with respect to FIG. 4. FIG. 4 illustrates a portion of an exemplary DSLAM 34 located within an RT or CO 30. The RT or CO 30 is provided with a protection panel 40 comprising at least one surge plug 42. A telephone line 22 from a subscriber""s premises 18 comprises POTS and xDSL signaling. The telephone line 22 enters the RT or CO 30 and through the protection panel 40 to an xDSL modem circuit 44. A POTS filter 46 (e.g., a high pass filter) can pass the xDSL transmission to the xDSL modem circuit 44 for processing. The xDSL modem converts the signal to data packets or asynchronous transfer mode (ATM) cells which are forwarded to a data switch, router or multiplexer. The line 48 from the protection panel 40 also provides the POTS and xDSL signaling from the subscriber""s premises to POTS-only circuits. A POTS splitter 38 passes the POTS signals which are then sent through the protection panel, as indicated by the line 50 to a CB 32.
Existing DSLAMs 34 incorporating internal POTS splitters 38 have several disadvantages and therefore present a number of drawbacks to implementing xDSL transmissions in subscriber loops. POTS splitters are generally passive devices comprising an inductive coil. The coil is generally large with respect to printed circuit board (PCB) area on which the POTS splitter and other POTS circuitry is provided. Optimization of PCB area is important to minimize the volume or space within the chassis of the termination equipment enclosing the PCB.
The size of the chassis of a DSLAM 34 or RAM is a concern of vendors for telecommunications equipment since their customers (e.g., telephone service providers) have a limited amount of rack space at their COs and in their RTs, as stated previously. In other words, the larger the profile of the DSLAM chassis, for example, the more rack space that is required at the CO or RT to accommodate DSL service using that vendor""s DSLAM, and the more likely that the smaller DSLAMs of competing vendors will be chosen. For example, a POTS splitter can require on the order of 2.5 cubic inches of PCB area. Reducing size of the coil in the POTS splitter is not a desirable option since the effectiveness of a POTS splitter can be compromised. A high inductance with a high quality or Q factor is desirable for a coil in a POTS splitter.
In addition to consuming valuable space within a DSLAM 34, internal POTS splitters 30 are problematic because the filtering of high frequency signals (e.g., xDSL signals) inside a DSLAM can present electromagnetic interference problems with xDSL circuitry 44 in close proximity to the POTS splitters 38. Also, POTS signals routed through the DLSAM 34 are lightning-exposed. Thus, POTS splitters require large clearances, in addition to the PCB area and DSLAM internal volume taken by virtue of their size. POTS splitters therefore preclude the use of fine-pitch front panel connectors to reduce the consumption of front panel space (e.g., the face plate of the DSLAM when rack mounted) and PCB area. Accordingly, a need exists for DSL equipment such as a DSLAM or RAM that economizes space at an RT and CO.
An existing central office POTS splitter that is externally mounted with respect to a DSLAM is commercially available. The POTS splitter is provided with other POTS splitters in a rack mountable chassis. A chassis that supports as many as 72 tip and ring pairs is on the order of nine inches high and therefore consumes considerable rack space. Thus, a need exists for POTS splitters that are externally mounted with respect to both the DSLAM and the racks in an RT or CO.
In addition to the size and space considerations of using internal or external, rack-mounted, POTS splitters, existing DSLAMs 34 are characterized by other drawbacks. For example, lightning trace clearances also consume significant PCB routing resources and require large-pitch, board-to-board PCB connectors. In addition, tip and ring lines routed through a DSLAM are individually fused using lightning-tolerant fuses to prevent surges from causing hazardous conditions within the DSLAM, resulting in two large fuses per port within the DSLAM. Thus, a need exists for a DSLAM which reduces the space and routing resources consumed by protection devices such as fuses and PCB routing and connectors having lightning trace clearance.
Another problem is presented when servicing existing DSLAM. To service a DSLAM, the xDSL cable is disconnected from the DSLAM (e.g., from the DSLAM connector 52, resulting in the interruption of POTS connections (e.g., line 54 in FIG. 4). In addition, the DSLAM connector 52 transports twice as many signals than is necessary. In other words, the connector 52 carries POTS and xDSL tip/ring pairs from the customer premises (e.g., from line 48), and POTS-only tip and ring signals routed to the CB (e.g., via line 50). A need exists for a DSLAM configuration that reduces the DSLAM connector ports consumed by POTS-only signals to increase the number of xDSL ports that can be terminated at a DSLAM in a given amount of rack space.
In accordance with the present invention, a system for externally mounting POTS splitters with respect to a DSLAM and to RT and CO equipment racks is provided which overcomes the deficiencies of existing DSLAMs and realizes a number of advantages.
In accordance with an embodiment of the present invention, the POTS splitters are provided, along with protection devices, to in-line sockets of a cable connecting both the telephone line from customer premises and the DSLAM to a protection panel mounted in the RT cabinet or proximally to a CO rack. Thus, the POTS splitters are arranged so as not to consume rack space.
In accordance with another embodiment of the present invention, a number of cables are terminated into an enclosure having multiple ports for respective cables. A multiport POTS splitter is provided, as well as a corresponding number of surge plugs for the respective ports. A single xDSL-only port is provided in the enclosure for a cable extending from the enclosure to a DSLAM.
In accordance with yet another embodiment of the present invention, an enclosure is provided with multiple ports for connection to telephone lines from subscribers"" premises. A surge plug is externally mounted to the enclosure for each port, and a multiport POTS splitter is provided internally. A single xDSL-only cable extends from the enclosure to a DSLAM.
In accordance with still yet another embodiment of the present invention, an integrated protection panel is provided which comprises a plurality of modules for connecting to respective customer premises. Each module comprises a surge protector and a POTS splitter, as well as ports for connecting to the telephone line from the customer premises, a POTS-only line to the channel bank and a line to the DSLAM.